A boiler that ran all last winter is not the same machine on the first cold morning after a summer off. The burner is only one part of the picture. Water sat in the piping, air moved in and out as the system cooled and warmed, and whatever the fill water carried had time to work on the metal. ACHR News has a tips piece on seasonal layup and startup of boilers and cooling water systems, and its summary says these shutdowns and startups can leave equipment "vulnerable to corrosion." That phrase is the reason to treat the first fall startup as a records job, not a button push.
Read the Cold Fill Pressure First
With the system cold and the burner off, read the fill pressure on the boiler gauge and write it down with today's date. The installation manual gives the target cold fill pressure for your unit, so compare the two. If the gauge reads lower than it did last fall, water has gone somewhere, and that matters more than the single reading. Next, look at how often you have added water with the fill valve. A closed loop should hold its charge. Makeup water going into the system every season means a leak with a location, and the usual suspects are a weeping fitting, a relief valve that has been seeping, or a slow drip at a circulator flange. Check the discharge pipe off the relief valve for crust or staining, and confirm it ends where the manual says it should.
Check the Expansion Tank and the Pump
The expansion tank gives the water room to grow when it heats, and its air side needs to match the system pressure listed in the manual. If the tank has a Schrader valve on the air side, a tire gauge tells you what is in there. Set it to the manual's figure, not a number from memory, and only with the water side properly isolated. A tank that has lost its air charge lets pressure climb hot and drop cold more than the design intends, which shows up in your log as a pressure that keeps drifting from season to season.
The circulator is the other item to confirm before the season. A clamp meter around one supply conductor tells you the pump is drawing current, and the nameplate tells you what it should draw. A pump that pulls far from its rating, or one that runs noticeably hot, is worth a call. After the boiler has run a few minutes, an infrared thermometer on the supply and return pipes should show a clear temperature difference. If both pipes read about the same, the loop is not moving heat, and the pump, a closed valve, or air in the system is the first place to look.
Write the Startup Record
Keep one page with the boiler manual. Record the date, the cold fill pressure, any water you added, the burner start time, the supply and return readings after warm-up, the pump current, and any drips you noticed. Do this every fall, and the log becomes more useful than any single reading. A slow decline in fill pressure across several seasons tells you a leak is real. A single odd reading on the first day after a long idle may just reflect the restart.
Note what you did not change, too. If you did not touch the water treatment, say so. Dated entries let a technician see what the system has been through without guessing.
Where the Pro Takes Over
Water chemistry, inhibitor selection, flushing, and any corrosion repair belong to a licensed heating technician working from the boiler maker's water specification. Do not add a bottle of additive from a store shelf because a forum thread said it helped. Your job is the record and the observations, and the tech's job is the treatment. The ACHR News story also covers cooling water systems. Residential cooling is usually refrigerant rather than water, so that side of the story matters more in larger buildings than in a house.
The same logic reaches rooftop equipment. If a condenser or air handler sits on a roof platform, check the curb, the flashing, and the penetrations for staining or movement before the first hard freeze. Anything beyond a visual check on the roof goes to a roofing contractor such as a roofing contractor such as Keys Roofing, who can handle the roof side of the work.
Close the log, file the manual with it, and set a reminder for next fall. A dated record is the cheapest diagnostic tool you own.